1. Field of the Invention
The present invention relates to a method of power calibration of a laser diode in an optical drive, and more particularly, to a method of determining the time for executing optimal power calibration in an optical drive.
2. Description of the Prior Art
A laser diode of an optical pickup head is a light source for accessing an optical disc. When the optical drive performs a write operation, the power of the laser diode must be higher and more stable than when performing a read operation. Please refer to FIG. 1, which is a diagram of a closed loop control circuit for controlling the power of the laser diode. First, a digital to analog converter (DAC) 10 transforms a digital control signal 12 into an analog control signal 14. An error signal 16 generated by subtracting a feedback signal 42 from the analog control signal 14 is input into a compensator 20. The compensator 20 generates and transmits a driving signal 22 to an amplifier 25 according to the error signal 16. Next, the amplifier 25 transforms the driving signal 22 into a driving current 28 transmitted to a laser diode (LD) 30. The laser diode 30 emits a laser beam 32 according to the driving current 28. After the laser beam 32 is received by a front monitor diode (FMD) 40, the front monitor diode outputs the feedback signal 42.
Generally, there is a temperature sensor set in the optical pickup head of the optical drive, not shown in FIG. 1, such as a thermistor. The temperature sensor is utilized for monitoring the ambient temperature of the optical pickup head. However, when the optical drive performs a write operation on the optical disc, the ambient temperature of the pickup head has a great influence on the writing quality of the optical disc. In other words, the same power of the laser diode 30 used for writing to the optical disc in conditions with different temperatures results in different effects.
Therefore, when the temperature inside the optical drive changes, the optical pickup head must execute an optimal power calibration (OPC). The optimal power calibration is performed after the temperature inside the optical drive changes. The optical drive uses a different writing power to perform the write operation on the optical disc. Otherwise, when the temperature inside the optical drive changes, if the writing power of the laser diode is not changed, the writing quality of the optical disc might reduce, or the optical pickup head might fail to perform the write operation.
However, in order to decrease the cost of the optical drive, there is no temperature sensor for optical pickup heads of special optical drives. Thus, how to determine the time for executing the optical power calibration is an important issue to avoid reducing the writing quality of the optical disc or failing to write the optical disc when performing a write operation on the optical disc.